1. Field of the Invention
The present invention relates to a transmission-type, scanning charged-particle beam microscope which includes a television camera tube and a television display tube for generating and displaying a diffraction image of a specimen to be examined.
2. Description of the Prior Art
Transmission-type, scanning electron microscopes in which pictorial display of the diffraction image is achieved by use of a television camera tube and a television monitor tube synchronized with the camera tube are known in the art. See, for example, U.S. Pat. No. 3,849,647. Due to the storage characteristic of the target of the television camera tube, the camera tube and the monitor tube comprise a parallel-operating detector system by means of which the entire diffraction image can be simultaneously detected. Such detector systems produce substantially better signal-to-noise ratios than the otherwise customary detection systems in which the diffraction image is sequentially scanned and displayed by a detector. If the scanning frequency of the television camera tube is high relative to the field frequency, diffraction images of the areas which are permeated during scanning are produced. However, if the scanning frequency of the television camera tube is approximately equal to the field frequency, a superposition of many partial diffraction images of the scanned area is produced on the television monitor tube.
The above-referenced U.S. patent discloses a transmission-type, scanning electron microscope in which a bright-field detector is disposed above the television camera tube and the output signal of the detector is transmitted to a second television monitor tube which is synchronized with the specimen scanning. The diffraction image and the bright-field image produced by the microscope can thus be observed simultaneously. The disadvantage of this arrangement, however, is that it is impossible to generate a dark-field image using such a system.